Semi-synthetic kratom derivatives in the Czech online market prior to regulatory reform: a baseline surveillance study.

Background: Semi-synthetic kratom derivatives, particularly 7-hydroxymitragynine (7-OH) and mitragynine pseudoindoxyl (MP), have raised regulatory and public health concerns due to their greater potency and associated risks. Their presence in European markets remains unexplored.Objective: This study assessed the availability and characteristics of semi-synthetic kratom products (SKPs) marketed online in the Czech Republic prior to implementation of the psychomodulatory substances framework in November 2025.Methods: We systematically searched Google and Seznam using predefined Czech kratom- and purchasing-related keywords to identify online vendors selling SKPs. Of 147 websites screened, product-level data were collected for semi-synthetic formulations containing 7-OH, MP, or both.Results: Eight websites (5.4%) offered SKPs, comprising 41 product listings with 22 distinct SKPs. Most SKPs reported 7-OH as the active semi-synthetic compound, while only 2 claimed to contain MP exclusively. Combination formulations included varying ratios of 7-OH and mitragynine. Most solid oral products contained 15-25 mg of semi-synthetic content per unit, although some reported up to 970 mg per unit. Most listings (n = 36; 87.8%) featured effect-related marketing claims. A substantial proportion (n = 29; 70.7%) were marketed as "collector's items" and not intended for human consumption.Conclusion: Prior to implementation of the new regulatory framework, semi-synthetic kratom derivatives were marketed online in the Czech Republic under regulatory ambiguity. Failure to distinguish between marketing of SKPs and natural kratom may increase consumer risk since it obscures substantial differences in their potency and pharmacological effects. These findings provide an important baseline for evaluating the impact of the Czech psychomodulatory substances framework.